Electrical connectors are used in many electronic systems. As miniaturization of the electronic systems becomes more prevalent, the dimensions of the connector itself decrease but the number of signal circuits routed through the connector increases. This results in an increasing number of signals in the limited space of the connector. As the signal circuits are spaced closer and the transmission speed of the signals increases, electromagnetic interference (EMI) and crosstalk become a serious problem. It is desirable that the components of an interconnection path be optimized for signal transmission characteristics; otherwise, the integrity of the system will be impaired or degraded. Such characteristics include low inductance, increased current carrying capacity, suitable roll-off, and reduced ground bounce. Continuous efforts have been made to develop electrical connectors that have as little effect as possible on electronic system performance and integrity.
Inductance is one concern in designing a connector, particularly when that connector is to be used in a signal transmission portion of a high speed electronic system. An example of one such connector is a so called “board-to-board” connector. A board-to-board connector provides the electrical, and often mechanical interface between printed circuit boards (PCB's) in an electronic system. Such connectors often have an elongated housing defining an elongated array of receptacles or slots for receiving a mating edge of the printed circuit board, or a field of pins projecting from the surface of the PCB that are mated to a corresponding field of contact receptacles. In many applications, such connectors are mounted on two or more PCB's commonly referred to as “daughter boards”, which are mounted to a “mother board.”
An inductive effect results from the interconnection of the PCB's which acts to change the characteristic impedance of the circuit and thereby negatively affect the signal transmission capacity of the system. Accordingly, it is desirable to reduce the inductive effects due to the interconnection of the PCB's, and thereby fulfill a need for an interconnection system that reduces inductive effects between the boards being connected. It would also be desirable to increase the current carrying capacity between the PCB's. Examples of such prior art board-to-board connectors may be found in U.S. Pat. Nos. 6,790,048; 6,776,668; 6,733,305; 6,729,890; 6,609,914; 6,599,138; 6,464,515; 6,338,630; 6,312,263; 6,183,315; 6,089,883; 6,220,903; 6,059,610; 6,036,504; 5,921,787; 5,876,219; and 5,873,742, which patents are hereby incorporated herein by reference.
Electrical connectors are often used in environments where they are exposed to dust and dirt, and may even be used in environments where they are subject to splash or immersion in water. It is desirable to seal the connector assembly to protect the terminals from exposure to the external environment. Very often the connector bodies are each formed with a plurality of passages that extend into the connector bodies from a cable end, and into which the cables and their terminals are received. In a sealed connector application, a seal is provided about the cable such that, when installed in the corresponding passage, it serves to seal the passage from the outside environment. The connectors are also sometimes filled with a potting material which will cover the rear entry of the electrical connector so as to protect it from the ingress of contaminants. It is necessary to prevent the entry of contaminants into the interior of the electrical connector, since these contaminants corrode the electrical contact surfaces which often leads to intermittent or unreliable electrical connections. Many types of seals and sealed connector systems are known for keeping contaminants from entering an electrical connector housing. Examples of such prior art sealed connector systems may be found in U.S. Pat. Nos. 6,821,145; 6,767,250; 6,547,584; 6,383,003; 6,132,251; 6,109,945; 6,050,839; 5,823,824; 5,785,544; 5,775,944; 5,595,504; 5,356,304; 4,983,344; 4,961,713; 4,944,688; 4,934,959; 4,895,529; 4,832,615; 4,776,813; 4,772,231; 4,085,993; 4,150,866; and 4,639,061, which patents are hereby incorporated herein by reference.
All of the foregoing connector systems rely upon one or more resilient conductive contacts having a variety of shapes, sizes, and spring characteristics. A commonly used form of resilient conductive contact includes an interconnection end for matting with a corresponding end of a mating contact or PCB, and a termination end for terminating a circuit trace or wire. These ends are often connected by a resilient portion of the contact which provides for the storage of elastic energy. Prior art resilient conductive contacts may be a single metal structure in the form of a spring to provide the required elastic response during service while also serving as a conductive element for electrical connection. Typically, a combination of barrier metal and noble metal platings are applied to the surface of the spring for corrosion prevention and for electrical contact enhancement. It is often the case that these platings are not of sufficient thickness for electrical conduction along only the surface of the spring. Examples of such prior art resilient conductive contacts may be found in U.S. Pat. Nos. 5,653,598; 5,173,055; 5,059,143; 4,906,194; 4,927,369; 4,699,593; and 4,354,729, which patents are hereby incorporated herein by reference.
One problem in the art exists in that a good material for the construction of a spring, such as a high strength steel, is not a very good electrical conductor. On the other hand, a good electrical conductor, such as a copper alloy or precious metal, often does not provide adequate spring properties. There has been a need in the connector arts for a more resilient conductive contact which incorporates the seemingly opposing requirements of good spring properties, temperature resistance, and high conductivity. Therefore, an improved electrical contact for use in an electrical connector is needed which can overcome the drawbacks of conventional electrical contacts. It is desirable that a good electrical contact element possess the following attributes: (a) usable in a wide variety of inter-connection structures; (b) a large elastic compliance range and low contact forces; (c) capable of transmitting high frequency signals and high currents; (d) capable of withstanding high operating temperatures; and (e) exhibiting high durability, i.e. >500K repeated deflections.
The prior art has been devoid of at least one of the foregoing attributes necessary for a universally applicable electrical connector.